Normally, the thread of the screw is half a millimeter and the disk is divided into 500 parts; in our exemplar the thread is 0.3774 mm and the disk is divided into 100 parts.
The thin edge of the disk acts as the index for the graduated scale adjacent to the disk on which the number of turns of the screw are read, while the angle of the scale adjacent to the disk, it too made thin, acts as the index for the graduation of the disk and allows evaluation of fractions of revolutions.
It is possible to produce micrometric screws so precise and without play as to allow appreciation on the disk of a ten-thousandth of a millimeter, but it is far more difficult to establish with the same precision the instant of contact of the point with the supporting plane.
The model presented here, when not in use, is placed on a wooden disk with three small indentures for the points supporting the instrument and is protected by a glass jar open at the top; the jar is covered by the plate of glass that acts as the supporting plane during measuring operations.